Robert Puentes of the Brookings Institution has described six ways the region could create a dedicated source of money for Metro:

* Gas taxes. Transit advocates consider them a logical way to raise money. But with the increased fuel economy of new vehicles, gas taxes across the nation have hit a plateau, and political leaders are reluctant to raise them.

* Sales taxes. A large amount of revenue can be raised with a small increase. But critics oppose them as regressive because they take a greater share of income from poor people.

* Congestion charges. They are levied when a motorist drives into a congested region or onto a crowded roadway during rush periods. Officials in Maryland and Virginia are considering express toll lanes on the Capital Beltway; motorists not in car pools would pay a toll to travel in an express lane.

* Parking taxes. The idea has been floated in the region for 40 years but never executed because of political resistance.

* Land-value capture. A special assessment could be levied on real estate around Metro stations, land that typically increases in value once a station is built. Los Angeles, Miami and Denver have such taxes.

* Payroll taxes. These taxes on earnings would be assessed at the place of employment instead of residence. In this region, a 0.5 percent payroll tax would generate enough revenue to cover the $412 million paid in local subsidies to Metro, according to Puentes.